In the case where substrates such as silicon wafer or the like are subjected to heat treatment with a vertical-type heat treating furnace, it is well known to control the output of a heater provided around a reaction chamber in order to have substrate temperatures approaching a set temperature (target value).
For example, Patent Document 1 discloses control of the outputs of heaters on the basis of thermal interference, to which substrates in a reaction chamber are subjected from a plurality of the heaters, and errors of substrate temperatures relative to a set temperature.
In the case where substrates being processed are large in size, however, there is in some cases generated a large difference between temperature changes detected in the reaction chamber and temperature changes in substrates.    Patent Document 1: JP-A-2002-175123